Optical seeking method and apparatus with track counting using tracking error signal having constant amplitude during data segments

ABSTRACT

There is disclosed a method for moving an optical head from an initial track to a target track on a storage medium. The total number of tracks to be crossed is determined, and the optical head is moved toward the target track. A reflectivity level of light from the storage medium is measured, and a tracking error signal is derived from the reflectivity level. The tracking error signal has both true and false indicators of track crossings. A data indicator signal is derived from the reflectivity level, having indicator points corresponding to the false indicators of track crossings. A track count number is incremented for each true indicator of a track crossing, and the optical head is stopped when the track count number equals the total number of tracks to be crossed. Another method is disclosed whereby a track count signal is generated from the tracking error signal and the data indicator signal. The track count signal indicates track crossings corresponding to the true track crossing indicators in the tracking error signal. An apparatus is disclosed comprising a sensor for measuring the reflectivity level from a storage medium, a tracking error signal generator for generating a tracking error signal, a preamplifier for generating a data signal, a track crossing signal generator responsive to the tracking error signal, and a track/hold selector responsive to the data signal to direct the track crossing signal generator to generate a track crossing signal without the false track crossing indicators from the tracking error signal. A second apparatus is disclosed comprising a sensor for measuring the reflectivity level from a storage medium, a preamplifier for generating a data signal, a tracking error signal generator responsive to the reflectivity level for deriving a tracking error signal, a track/hold selector to direct the tracking error signal generator to generate a signal of constant amplitude for a predetermined period of time based on the data signal, and a track crossing signal generator responsive to the tracking error signal for deriving a track crossing signal indicating the crossing of an information track by the optical head.

This is a division of application Ser. No. 08/418,723, filed Apr. 7,1995, pending.

FIELD OF THE INVENTION

The invention relates to optical systems, and, in particular, to seekingby an optical head in an optical system.

DESCRIPTION OF THE BACKGROUND ART

Certain types of storage media have constant reflectivity levels in thedata storage areas. Data differentiation may be accomplished by phasecomparison or other suitable methods. Other areas on the storage media,such as headers, may have differing reflectivity levels.

In seeking from one track to another, a track crossing number isdetermined. The track crossing number indicates the number of tracks tobe crossed in seeking from an initial track to a target track. When theseek is performed, an actual track crossing count is kept, indicatingthe number of tracks crossed so far. When the actual track crossingcount equals the track crossing number, the seek is finished and thetarget track has been reached.

In prior art systems, the actual track crossing count could be derivedfrom the tracking error signal. However, if the path of a seek crossedthe areas having differing reflectivity levels, the tracking errorsignal would erroneously indicate that a track had been crossed.Therefore, if the actual track crossing count relied on the trackingerror signal, it would equal the track crossing number before the targettrack had been reached, causing undershoot of the seek and requiringeither another seek or a seek correction.

SUMMARY OF THE INVENTION

A method is disclosed for moving an optical head from an initial trackto a target track on a storage medium. The total number of tracks to becrossed is determined, and the optical head is moved toward the targettrack. A reflectivity level of light from the storage medium ismeasured, and a tracking error signal is derived from the reflectivitylevel. The tracking error signal has both true and false indicators oftrack crossings. A data indicator signal is derived from thereflectivity level, having indicator points corresponding to the falseindicators of track crossings. A track count number is incremented foreach true indicator of a track crossing, and the optical head is stoppedwhen the track count number equals the total number of tracks to becrossed. Another method is disclosed whereby a track count signal isgenerated from the tracking error signal and the data indicator signal.The track count signal indicates track crossings corresponding to thetrue track crossing indicators in the tracking error signal. Anapparatus is disclosed comprising a sensor for measuring thereflectivity level from a storage medium, a tracking error signalgenerator for generating a tracking error signal, a preamplifier forgenerating a data signal, a track crossing signal generator responsiveto the tracking error signal, and a track/hold selector responsive tothe data signal to direct the track crossing signal generator togenerate a track crossing signal without the false track crossingindicators from the tracking error signal. A second apparatus isdisclosed comprising a sensor for measuring the reflectivity level froma storage medium, a preamplifier for generating a data signal, atracking error signal generator responsive to the reflectivity level forderiving a tracking error signal, a track/hold selector to direct thetracking error signal generator to generate a signal of constantamplitude for a predetermined period of time based on the data signal,and a track crossing signal generator responsive to the tracking errorsignal for deriving a track crossing signal indicating the crossing ofan information track by the optical head.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a generalized representation of a storage medium adaptable foruse with the invention.

FIG. 2 is an enlargement of a portion of the storage medium shown inFIG. 1.

FIG. 3 is a generalized representation of a storage medium adaptable foruse with the invention, showing the path traveled by the optical headduring a seek.

FIG. 4 is a generalized representation of one embodiment of theinvention.

FIG. 5 is a generalized plot of waveforms generated by one embodiment ofthe invention

FIG. 6 is a generalized representation of another embodiment of theinvention.

FIG. 7 is a generalized plot of waveforms generated by anotherembodiment of the invention

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to exemplary FIG. 1, there is shown a generalizedrepresentation of a storage medium 1 adaptable for use with theinvention. The storage medium 1 has a center 2 and data is recordedthereon in information tracks 3 concentric about the center 2. Theinformation tracks 3 may be arranged in a spiral about the center 2.Data is further arranged in sectors 4 separated by radial (ornon-radial) sector headers 5.

Referring to exemplary FIG. 2, there is shown an enlargement of aportion of the storage medium 1 shown in exemplary FIG. 1. Intertrackregions 6 are located concentrically between consecutive informationtracks 3. Data may be recorded in segments 7 where the informationtracks 3 intersect the sectors 4. Additionally, there is data in headersegments 8 where the information tracks 3 intersect the radial (ornonradial) sector headers 5. This data in the header segments 8 iseither embossed or otherwise not modifiable by the optical system.

Referring to exemplary FIG. 3, there is shown a generalizedrepresentation of the storage medium 1 shown in exemplary FIG. 1.Additionally, the storage medium 1 is rotating about the center 2 in thedirection indicated by arrow 9. To perform a seek from an initialinformation track 10 to a target information track 11, an optical head(not shown) will travel on a path 12 relative to the storage medium 1.In traveling along the path 12, the optical head (not shown) will crossradial sector headers 5 at intersection points 13.

Referring to exemplary FIG. 4, there is shown one embodiment of theinvention. The apparatus comprises a sensor 14 for detecting areflectivity level of light reflected from the storage medium 1. Thesensor 14 passes the reflectivity level to a preamplifier 15. Thepreamplifier 15 generates a data signal which is indicative of changesin the reflectivity level in response to data located in the informationtracks 3. The preamplifier 15 may contain a high pass filter, throughwhich the data signal is passed. The preamplifier 15 then passes thedata signal to a track/hold selector 16.

The sensor 14 also passes a signal representing a returning opticalpattern to a tracking error signal generator 17. Tracking error can be,and usually is, generated by split or quad detectors. Quad sum detectors(outputting the sum signal of the quad detectors) for servos can alsogenerate track crossing indications. As shown in FIGS. 5 and 7, a"bipolar" signal, generated by split detectors in push pull representsthe pattern produced by interference fringes. The tracking error signalgenerator 16 derives a tracking error signal. The tracking error signalindicates changes in the reflectivity level both in response to datalocated in the information tracks 3 and in response to the optical head(not shown) crossing an information track 3. The tracking error signalgenerator 17 then passes the tracking error signal to the track/holdselector 16.

The track/hold selector 16 generates a control signal in response to thedata signal. The track/hold selector 16 then passes the control signaland the tracking error signal to a track crossing signal generator 18.The track crossing signal generator 18 creates a track crossing signalin response to the tracking error signal. The track crossing signal is agenerally a square waveform corresponding to the tracking error signal.The control signal directs the track crossing signal generator 18 toignore the portions of the tracking error signal corresponding toportions of the data signal indicating changes in the reflectivity levelin response to data located in the information tracks 3. The trackcrossing signal generator 18 thus generates a track crossing signalindicating changes in the reflectivity level in response to the opticalhead (not shown) crossing an information track 3.

In operation, a seek is performed from the initial track 10 to thetarget track 11. A track crossing number is generated, which is equal tothe number of tracks between the initial track 10 and the target track11. The optical head (not shown) is moved from the initial track 10toward the target track 11. The embodiment of the invention, asdescribed above, responds to light reflected off the storage medium i togenerate a track crossing signal. A track crossing counter (not shown)counts the number of changes in the reflectivity level indicated in thetrack crossing signal. When the track crossing counter equals the trackcrossing number, the optical head (not shown) has reached the targettrack 11.

Referring to exemplary FIG. 5, there are shown the waveforms of thesignals created by components of the above-described embodiment. Each ofthe waveforms is plotted against time on the horizontal axis, with thebeginning of the seek at the left and the end of the seek at the right.The time segment 19 indicates a point when the optical head (not shown)is crossing a header segment 8.

In line 51, there is shown a waveform 20 of the tracking error signalgenerated by the tracking error signal generator 17. The waveform 20 haszero crossings 21 indicating that the optical head (not shown) hascrossed an information track 3. The waveform segment 22 during the timesegment 19 shows that the reflectivity level changes in response to datawithin the header segment 8. Because the waveform segment 22 has zerocrossings 23, the tracking error signal, if not corrected, wouldgenerate a false track crossing counter number, causing the optical head(not shown) to stop seeking before reaching the target track 11.

In line 52, there is shown a waveform 24 of the data signal generated bythe preamplifier 15. The waveform 24 plots the sum reflectivity levelfrom the storage medium 1. As shown, the waveform 24 is relatively flatexcept at a waveform segment 25 during the time segment 19. Where datawithin the header segment 8 may cause changes in the sum reflectivitylevel. The data signal therefore indicates the time segment 19 by thewaveform segment 25.

In line 53, there is shown a waveform 26 of an uncorrected trackcrossing signal generated by a track crossing signal generator accordingto the prior art. The waveform 26 has zero crossings 27 corresponding tothe zero crossings 21 of the waveform 20 of the tracking error signal.However, the waveform 26 also has zero crossings 28 corresponding to thezero crossings 23 of the waveform 20 of the tracking error signal. Thesezero crossings 28, however, are not indicative of the optical head (notshown) crossing an information track 3. A track crossing counter isbased on the number of zero crossings 27, 28 in the waveform 26 of thetrack crossing signal generator. However, using the waveform 26 fromline 53, the track crossing counter would be inaccurate because therewould be no differentiation between zero crossings 27 indicating that aninformation track 3 is crossed and zero crossings 28 responsive to datain the header segments 8.

In line 54, there is shown a waveform 29 of a corrected track crossingsignal generated by the track crossing signal generator 18 according tothe invention. The track crossing signal generator 18 only generates azero crossing 30 when both of the following conditions are satisfied.First, the waveform 20 of the tracking error signal must indicate a zerocrossing 21. Second, the waveform 24 of the data signal must notindicate that data from the header segment 8 is causing the zerocrossing 23. If both conditions are satisfied, the track crossing signalgenerator 18 generates a zero crossing 30. Therefore, a track crossingcounter can count the number of zero crossings 30 in the waveform 29 ofthe track crossing signal to determine the number of information tracks3 the optical head (not shown) has crossed

Referring to exemplary FIG. 6, there is shown a second embodimentaccording to the invention. The apparatus comprises a sensor 14 fordetecting a reflectivity level of light reflected from the storagemedium 1. The sensor passes the reflectivity level to a preamplifier 15.The preamplifier 15 generates a data signal which is indicative ofchanges in the reflectivity level in response to data located in theinformation tracks 3. The preamplifier 15 may contain a high passfilter, through which the data signal is passed. The preamplifier 15then passes the data signal to a track/hold selector 31.

The track/hold selector 31 generates a control signal in response to thedata signal. The track/hold selector 31 generates a control signal inresponse to the data signal. The track/hold selector 31 passes thecontrol signal to a tracking error signal generator 32. The sensor 14also passes the reflectivity level to the tracking error signalgenerator 32.

The tracking error signal generator 32 generates a tracking error signalin response to the reflectivity level from the sensor 14 and in responseto the control signal from the track/hold selector 31. When the datasignal does not indicate that changes in the reflectivity level are inresponse to data located in the information tracks 3, the control signaldirects the tracking error signal generator 32 to generate the trackingerror signal in a standard manner known in the art. However, when thedata signal indicates that changes in the reflectivity level are inresponse to data located in the information tracks 3, the control signaldirects the tracking error signal generator 32 to generate a flatwaveform for a short period of time. The tracking error signal generator32 then passes the tracking error signal to a track crossing signalgenerator 33.

The track crossing signal generator 33 generates a track crossingsignal, which is a square waveform from the tracking error signal. Thetrack crossing signal indicates the number of changes in thereflectivity level indicated in the tracking error signal. A trackcrossing counter (not shown) counts the number of changes in thereflectivity level indicated in the track crossing signal. When thetrack crossing counter equals the track crossing number, the opticalhead (not shown) has reached the target track 11.

Referring to exemplary FIG. 7, there are shown the waveforms of thesignals created by components of the second above-described embodiment.Each of the waveforms is plotted against time on the horizontal axis,with the beginning of the seek at the left and the end of the seek atthe right. The time segment 34 indicates a point when the optical head(not shown) is crossing a header segment 8.

In line 71, there is shown a waveform 35 of the data signal generated bythe preamplifier 15. The waveform 35 plots the sum reflectivity levelfrom the storage medium 1. As shown, the waveform 35 is relatively flatexcept at a waveform segment 36 during the time segment 34. Where datawithin the header segment 8 may cause changes in the sum reflectivitylevel. The data signal therefore indicates the time segment 34 by thewaveform segment 36.

In line 72, there is shown a waveform 37 of an uncorrected trackingerror signal generated by a tracking error signal generator according tothe prior art. The waveform 37 has zero crossings 38 which correspond tochanges in the reflectivity level in response to the optical head (notshown) crossing an information track 3. The waveform also has a waveformsegment 39 corresponding to the time segment 34 when the optical head(not shown) is crossing a header segment 8. The waveform segment 39plots indicates changes in the reflectivity level in response to datawithin the header segment 8. The waveform segment 39 has zero crossings40 which correspond to those changes. A track crossing signal createdfrom this waveform 37 would appear similar to the waveform 26 in line 53of exemplary FIG. 5, and could not be relied on accurately by a trackcrossing counter.

In line 73, there is shown a waveform 41 of a corrected tracking errorsignal generated by the tracking error signal generator 32. The waveform41 is generated as follows. When the changes in the reflectivity levelare low frequency, the tracking error signal generator 32 generates atracking error signal in the standard manner known in the art. This isrepresented by a waveform segment 42. However, when the tracking errorsignal generator 32 detects a higher frequency change in thereflectivity level, corresponding to the waveform segment 39 in line 72,the tracking error signal generator 32 looks at the data signalrepresented by the waveform 35 in line 71. If the data signal is notflat, as in the waveform segment 36, the tracking error signal generator32 generates a flat waveform segment 43 at the amplitude of the trackingerror signal just prior to the detection of the high frequency changesin the reflectivity level. Once the changes in the reflectivity levelreturn to a lower frequency, the tracking error signal generator 32returns to generating the tracking error signal in the standard manner.

The waveform 41 of the corrected tracking error signal has zerocrossings 44 indicating that the optical head (not shown) has crossed aninformation track 3. Unlike the waveform 37 in line 72 of theuncorrected tracking error signal, the waveform 41 in line 73 of thecorrected tracking error signal does not have zero crossings during thetime segment 34 corresponding to the zero crossings 40. Therefore, thenumber of zero crossings 44 in the waveform 41 accurately indicates thenumber of information tracks 3 crossed by the optical head (not shown).

In line 74, there is shown a waveform 45 of a track crossing signalgenerated by the track crossing signal generator 33. The waveform 45 isa square waveform of the waveform 41 of the corrected tracking errorsignal generated by the tracking error signal generator 32. The waveform45 of the track crossing signal has zero crossings 46 corresponding tothe zero crossings 44 in the waveform 41 of the tracking error signal.Therefore, a track crossing counter can count the number of zerocrossings 46 in the waveform 45 of the track crossing signal todetermine the number of information tracks 3 the optical head (notshown) has crossed.

It will be obvious to one skilled in the art that modifications to theabove description of the invention may be made without departing fromthe spirit and scope of the invention. The scope of the invention,therefore, is indicated by the appended claims rather than the abovedescription.

What is claimed is:
 1. A method for moving an optical head from aninitial track to a target track on a storage medium having data arrangedin tracks thereon, comprising the steps of:determining a track crossingnumber indicating a number of said tracks between said initial track andsaid target track; moving said optical head from said initial tracktoward said target track; measuring a reflectivity level of light fromsaid storage medium; passing said reflectivity level through a high passfilter to obtain a data indicator signal, wherein a waveform of saiddata indicator signal has indicator points corresponding to changes insaid reflectivity level in response to said data; deriving a trackingerror signal responsive to said reflectivity level and said dataindicator signal, wherein a waveform of said tracking error signal haszero crossings corresponding to said optical head crossing one of saidtracks and constant amplitude segments corresponding to said indicatorpoints; incrementing a track count number for each first zero crossing;and terminating the step of moving said optical head when said trackcount number equals said track crossing number.
 2. A method for movingan optical head from an initial track to a target track on a storagemedium having data arranged in tracks thereon, comprising the stepsof:determining a track crossing number indicating a number of saidtracks between said initial track and said target track; moving saidoptical head from said initial track toward said target track; measuringa reflectivity level of light from said storage medium; passing saidreflectivity level through a high pass filter to obtain a data indicatorsignal, wherein a waveform of said data indicator signal has indicatorpoints corresponding to changes in said reflectivity level in responseto said data; deriving a tracking error signal responsive to saidreflectivity level and said data indicator signal, wherein a waveform ofsaid tracking error signal has zero crossings corresponding to saidoptical head crossing one of said tracks and constant amplitude segmentscorresponding to said indicator points; generating a track count signalfrom said tracking error signal, wherein a waveform of said track countsignal has track crossing points corresponding to said zero crossings;incrementing a track count number for each said track crossing point;and terminating the step of moving said optical head when said trackcount number equals said track crossing number.
 3. A method for movingan optical head from an initial track to a target track on a storagemedium having data arranged in tracks thereon, comprising the stepsof:determining a track crossing number indicating a number of saidtracks between said initial track and said target track; moving saidoptical head from said initial track toward said target track; measuringa reflectivity level of light from said storage medium; passing saidreflectivity level through a high pass filter to obtain a data indicatorsignal, wherein a waveform of said data indicator signal has indicatorpoints corresponding to increases in frequency of changes in saidreflectivity level; deriving a tracking error signal responsive to saidreflectivity level and said data indicator signal, wherein a waveform ofsaid tracking error signal has zero crossings corresponding to saidoptical head crossing one of said tracks and constant amplitude segmentscorresponding to said indicator points; incrementing a track countnumber for each first zero crossing; and terminating the step of movingsaid optical head when said track count number equals said trackcrossing number.
 4. A method for moving an optical head from an initialtrack to a target track on a storage medium having data arranged intracks thereon, comprising the steps of:determining a track crossingnumber indicating a number of said tracks between said initial track andsaid target track; moving said optical head from said initial tracktoward said target track; measuring a reflectivity level of light fromsaid storage medium; passing said reflectivity level through a high passfilter to obtain a data indicator signal, wherein a waveform of saiddata indicator signal has indicator points corresponding to increases infrequency of changes in said reflectivity level; deriving a trackingerror signal responsive to said reflectivity level and said dataindicator signal, wherein a waveform of said tracking error signal haszero crossings corresponding to said optical head crossing one of saidtracks and constant amplitude segments corresponding to said indicatorpoints; generating a track count signal from said tracking error signal,wherein a waveform of said track count signal has track crossing pointscorresponding to said zero crossings; incrementing a track count numberfor each said track crossing point; and terminating the step of movingsaid optical head when said track count number equals said trackcrossing number.
 5. A method for moving an optical head from an initialtrack to a target track on a storage medium having data arranged intracks thereon, comprising the steps of:determining a track crossingnumber indicating a number of said tracks between said initial track andsaid target track; moving said optical head from said initial tracktoward said target track; measuring a reflectivity level of light fromsaid storage medium; deriving a data indicator signal responsive to saidreflectivity level, wherein a waveform of said data indicator signal hasindicator points corresponding to changes in said reflectivity level inresponse to said data; deriving a tracking error signal responsive tosaid reflectivity level and said data indicator signal, wherein awaveform of said tracking error signal has zero crossings correspondingto said optical head crossing one of said tracks and constant amplitudesegments corresponding to said indicator points; incrementing a trackcount number for each first zero crossing; and terminating the step ofmoving said optical head when said track count number equals said trackcrossing number.
 6. A method for moving an optical head from an initialtrack to a target track on a storage medium having data arranged intracks thereon, comprising the steps of:determining a track crossingnumber indicating a number of said tracks between said initial track andsaid target track; moving said optical head from said initial tracktoward said target track; measuring a reflectivity level of light fromsaid storage medium; deriving a data indicator signal responsive to saidreflectivity level, wherein a waveform of said data indicator signal hasindicator points corresponding to changes in said reflectivity level inresponse to said data; deriving a tracking error signal responsive tosaid reflectivity level and said data indicator signal, wherein awaveform of said tracking error signal has zero crossings correspondingto said optical head crossing one of said tracks and constant amplitudesegments corresponding to said indicator points; generating a trackcount signal from said tracking error signal, wherein a waveform of saidtrack count signal has track crossing points corresponding to said zerocrossings; incrementing a track count number for each said trackcrossing point; and terminating the step of moving said optical headwhen said track count number equals said track crossing number.
 7. Amethod for moving an optical head from an initial track to a targettrack on a storage medium having data arranged in tracks thereon,comprising the steps of:determining a track crossing number indicating anumber of said tracks between said initial track and said target track;moving said optical head from said initial track toward said targettrack; measuring a reflectivity level of light from said storage medium;deriving a data indicator signal responsive to said reflectivity level,wherein a waveform of said data indicator signal has indicator pointscorresponding to increases in frequency of changes in said reflectivitylevel; deriving a tracking error signal responsive to said reflectivitylevel and said data indicator signal, wherein a waveform of saidtracking error signal has zero crossings corresponding to said opticalhead crossing one of said tracks and constant amplitude segmentscorresponding to said indicator points; incrementing a track countnumber for each first zero crossing; and terminating the step of movingsaid optical head when said track count number equals said trackcrossing number.
 8. A method for moving an optical head from an initialtrack to a target track on a storage medium having data arranged intracks thereon, comprising the steps of:determining a track crossingnumber indicating a number of said tracks between said initial track andsaid target track; moving said optical head from said initial tracktoward said target track; measuring a reflectivity level of light fromsaid storage medium; deriving a data indicator signal responsive to saidreflectivity level, wherein a waveform of said data indicator signal hasindicator points corresponding to increases in frequency of changes insaid reflectivity level; deriving a tracking error signal responsive tosaid reflectivity level and said data indicator signal, wherein awaveform of said tracking error signal has zero crossings correspondingto said optical head crossing one of said tracks and constant amplitudesegments corresponding to said indicator points; generating a trackcount signal from said tracking error signal, wherein a waveform of saidtrack count signal has track crossing points corresponding to said zerocrossings; incrementing a track count number for each said trackcrossing point; and terminating the step of moving said optical headwhen said track count number equals said track crossing number.